Studies will be conducted to standardize and quantify the experimental lesion produced in young animals by exposure to hyperoxia to further elucidate the role of oxygen in retrolental fibroplasia. The critical PaO2 levels associated with irreversible capillary closure will be determined. Anti-oxidants thought to counteract the oxygen toxic effect of oxygen will be tested in this model. Further studies will be conducted in an attempt to develop a better method of monitoring oxygen levels in the premature nursery.